The Era of Direct Imaging of Exoplanets Has Arrived

In this episode, astronomers are finally starting to get direct images of planets around other stars, and not only that, for the first time, ground-based telescopes are actually getting measurements of the atmospheres of these galactic neighbors.

Published on 25th Apr, 2019

Hello Space Fans and welcome to another edition of Space Fan News. In this episode, astronomers are finally starting to get direct images of planets around other stars, and not only that, for the first time, ground-based telescopes are actually getting measurements of the atmospheres of these galactic neighbors. Whenever we talk about exoplanets here on SFN or on one of our many hangouts that we have on new exoplanet discoveries, we always hear about looking at these planets via indirect methods, like the Transit Method, which measures tiny dips in the brightness of a star when a planet passes between us and the star. There’s also the radial velocity method where you look at a star’s light through a spectrograph and watch the spectral lines go back and forth as the planet tugs on the star in its orbit. There’s also weak gravitational lensing which causes a characteristic blip in the star’s light as the planet passes in front and bends that light through its gravitational field. All of these are indirect ways of seeing an exoplanet though, they aren’t direct pictures of the planets themselves. As you can imagine, these kinds of images are hard to take, the star is so much brighter than the planet itself that it completely blinds us when trying to see it. So the holy grail of exoplanet studies is direct imaging of these planets. When we can do that, then we can really study the details about the planet and learn some really key things like whether it has an atmosphere or if there are any biosignatures of life that we can tease out of the light signal. Now, believe it or not, we do have a direct image of a system of exoplanets. This is HR8799, which is 129 light years away in the constellation of Pegasus and is about 1.5 times the size of our sun. Three planets, roughly 10, 10 and 7 times the mass of Jupiter, orbit the star. The sizes of the planets decrease with distance from the parent star, much like the giant planets do in our system. And this was taken in 2008! There have been other direct images of exoplanets but this is the only multi planet system that we have images for and for a long time, this was the picture of the system. Three planets b, c, and d with d being the smallest at 7 times the mass of Jupiter. Then, in 2010, Keck found a fourth planet, HR8799e and it took a while I guess because it was really close to the star. It’s the smallest of the bunch with 7 times the mass of Jupiter that orbits its star every 200 years The other planets are 24, 37 and 67 AU from the host star. The furthest planet in the new system orbits just inside a disk of dusty debris, similar to that produced by the comets of the Kuiper belt of our solar system (FYI: Neptune is 30 AU). Here are seven years worth of observations showing the system. HR8799e is the closest and from the way Keck describes this, it looks like adaptive optics were used to steady the atmosphere, then a subtraction was made to get rid of the main star. Remember, these stars are huge, way bigger than Jupiter, which is one reason we can see them so well. The host star is a bright, blue A-type star, and also young – less than 100 million years old – which means its planets are still glowing with heat from their formation also helping us see them. But the story’s not over. Late last month, astronomers from ESO’s GRAVITY instrument managed to get some details about the innermost planet HR8977e by using ESO’s VLT’s four unit telescopes to work together to make a single larger telescope using a technique known as interferometry. This creates a super-telescope — the VLTI — that collects and precisely disentangles the light from HR8799e’s atmosphere and the light from its parent star. If this sounds familiar, this same technique was used by radio telescopes all over the world to create an Earth-sized telescope - the Event Horizon Telescope - that had enough resolution to see the black hole at the center of M87. Well, by using the VLT’s four unit telescopes in a really complicated way, they were able to measure some of the details of the atmosphere of HR8799e and as usual, there were surprises. First, they found way more carbon monoxide than methane, something that usually doesn’t happen. The CO usually equilibriates into methane and that didn’t happen here. They think maybe there are high vertical winds within the atmosphere preventing the carbon monoxide from reacting with hydrogen to form methane. This place also isn’t that hospitable. Temperatures are around 1000 degrees celsius so again, we won’t be moving there anytime soon, but the big news here is that this work can be done from the ground, using interferometry and adaptive optics. If you want to learn more about the VLT unit telescopes, we did a hangout a few weeks ago talking about the science and equipment at ESO so please check it out. Alright that is it for this episode Space Fans, thanks to OPT for sponsoring SFN, if you need a scope, please check em out and tell em I sent you! SFN is also made possible by all of Deep Astronomy’s Patreon Patrons, who’s kind generosity make all videos possible so thanks to all of you. And thank you for watching and as always, Keep Looking Up!